In a process for producing fibers, such as a synthetic fiber, it is quite conventional to adopt a method in which a yarn package transporting car or cars are employed for transporting undrawn yarn packages formed by a spinning machine to a so-called post processing machine in a subsequent process, such as a drawing machine, a draw-twisting machine and a draw-false-twisting machine. The method is very advantageous for promoting the transporting efficiency of the yarn packages. However, there has not yet been provided any automatic yarn package transporting method with a high labor-saving efficiency, in which method a series of operations, including doffing of undrawn yarn packages from a spinning machine, transporting of the doffed undrawn yarn packages, supplying of the undrawn yarn packages to a post processing machine, and returning of an emptied transporting cars after completion of the supplying of the undrawn yarn packages to the post processing machine, are organically interconnected.
Further, in order to realize a complete automation of a yarn package transporting method for the sake of heightening the production efficiency of diverse fibers, it is indispensably required for acquiring high quality fibers that, when a faulty portion of yarn is detected during the supplying of the yarns to a post processing machine in a drawing process, draw-twisting process or draw-false-twisting process, it can not only be easily confirmed which winding spindle of which spinning machine caused the detected faulty portion of the yarn, but also, the winding spindle that produced the faulty yarn portion can be quickly repaired.